Ni Grains Research Articles

Mg bulk and surface modification on Ni/Y2Ti2O7 catalyst for dry reforming of methane

Dry reforming of methane (DRM) can simultaneously convert two greenhouse gases, CH4 and CO2, into high value-added synthetic gas, which can effectively alleviate the energy crisis and optimize the human ecological environment. In this work, the effect of Mg addition method on the activity of the Y2Ti2O7 pyrochlore supported Ni catalysts was investigated in DRM. The H2-TPR and XPS results showed that Mg modification enhanced the interaction between Ni and Y2Ti2O7 pyrochlore support. Thus, much smaller Ni grains with better thermal stability could be achieved on the Mg doped Ni/Y2Ti2O7 catalyst, as evidenced by the XRD, H2-TPD and TEM results. CO2-assistant CH4-TPSR demonstrated that Mg surface modification can facilitate the reaction between the activated CO2∗ and the H∗ produced by CH4 dissociation. Mg incorporation increased the basic site of the Ni/Y2Ti2O7 catalyst, as evidenced by CO2-TPD-MS results, which was conducive to the adsorption and activation of CO2 to promote the removal of coke deposition. Consequently, Ni/Y1·5Mg0·5Ti2O7 and Ni–MgO/Y2Ti2O7 catalysts exhibit higher stability and more potent coke resistance than the unmodified Ni/Y2Ti2O7 sample. It is concluded that higher Ni0 dispersion and more mobile active oxygen species are the main reasons for the improvement of activity and coke resistance of the Ni/Y2Ti2O7 catalysts. In addition, in situ DRIFTS results confirmed that CO2 activation of all catalysts followed the formate intermediate species path.

Effect of alloying element segregation on theoretical strength and structural low-energy transition of Ni grain boundaries: A first-principles computational tensile test study

Enhancing the stability and strength of nanocrystalline metals through the manipulation of grain boundary (GB) chemistry and structure is crucial for their engineering applications. In this study, first-principle computational tensile tests on Ni Σ5 [001] (210) GBs were conducted with considering Poisson's ratio and strengthening effect of alloying elements B, W, Zr, Ta, B-W and Zr-Ta segregation. The results indicate that the Zr-Ta co-segregated GB shows a remarkable increase in theoretical tensile strength by 195 % compared to the clean GB under small strain conditions. As tensile strain increases, both clean and segregated GBs undergo a low-energy structural transition from the Σ5 [001] (210) to the more stable Σ11 [110] (113). This work presents a promising approach for enhancing the stability of Ni nanograined materials through tensile deformation and GB segregation.

A potential mechanism for abnormal grain growth in Ni thin films on c-sapphire

Normal grain growth (NGG) of a (111) textured Ni film on c-sapphire and abnormal grain growth (AGG) of (100) grains at the expense of this (111) texture has been studied as a function of temperature with and without a capping layer. The grain boundaries (GBs) in the Ni film are controlled by the preferred orientation relationships (ORs) adopted by the Ni grains on the sapphire substrate. The 2 variants of a single OR, Ni(111)<11¯0>//Al2O3(0001)<11¯00>, form a (111) mazed bicrystal with Σ3 GBs. The (100) grains have a single OR, Ni(100)<010>//Al2O3(0001)<11¯00> with 3 variants; their GBs within the (111) grains have the (111)<11¯0>//(100)<010> misorientation.(100) AGG within the (111) mazed bicrystal of the 100 nm Ni film takes place above 1023 K. The orientation transition is driven by the biaxial elastic modulus anisotropy which favors the growth of (100) grains over (111) grains, as this reduces the elastic strain energy induced by the thermal mismatch between Ni and sapphire. (100) AGG is suppressed and the NGG of the (111) texture is slowed down when the film is covered by a 10 nm amorphous alumina layer aimed at inhibiting surface diffusion. Thus, it is proposed that as long as the surface can act as a sink for the point defects diffusing along the GBs, the movement of the GBs is correlated to the diffusivity of atoms and vacancies, which is a function of their misorientation and crystallographic GB structure.

Grain boundary diffusion in additively manufactured CoCrFeMnNi high-entropy alloys: Impact of non-equilibrium state, temperature and relaxation

Grain boundary diffusion of Ni in the equiatomic CoCrFeMnNi high-entropy alloy, produced by additive manufacturing, is measured using a radiotracer technique in an extended temperature interval of 350 to 703 K. A strongly non-monotonic temperature dependence of the Ni grain boundary diffusion coefficients (with a spectacular intermittent retardation of the diffusion rates with increasing temperature) is seen and explained by relaxation of a non-equilibrium state induced by rapid solidification during fabrication. The grain boundary excess energy of the non-equilibrium state of these grain boundaries, as estimated from the diffusion data, is found to be larger than 0.3 J/m2. This corresponds to an increase of about 30% of the interface energy compared to relaxed general high-angle grain boundaries. The temperature-induced evolution of the grain boundary state is analyzed in terms of the concomitant structure evolution, segregation, phase stability and precipitation in the multi-component alloy.

2-Methylfuran hydrogenation to 2-methyltetrahydrofuran utilizing Ni/SiO2 catalysts in vapor-phase: Excellent stability via enhanced metal-support interaction

Biomass-derived 2-methyltetrahydrofuran (2-MTHF) is a significant green solvent and a promising biomass fuel, and it is usually produced from 2-methylfuran (2-MF) hydrogenation in liquid phase. It is highly desirable and challenging to develop vapor-phase hydrogenation with such a catalyst that combines high efficiency, excellent stability, easy scale up and low cost. In the present work, we prepared three Ni/SiO2 catalysts using impregnation, urea-assisted impregnation, and deposition–precipitation methods (labeled as NS-IM, NS-UIM, and NS-DP), respectively, for the synthesis of 2-MTHF from 2-MF hydrogenation in vapor-phase. The NS-DP catalyst demonstrated the highest activity and the best stability among all catalysts. Under moderate reaction conditions, a 2-MF conversion of 99.9% with a 2-MTHF selectivity of 99% were achieved on the NS-DP catalyst over 140 h, and it showed a potential significant application prospect. N2 physisorption, ICP, XRD, H2-TPR, TG, HRTEM, and in situ XPS characterization revealed that the catalyst prepared by the deposition–precipitation method possessed the smallest Ni grain size and the strongest metal-support interaction, leading to the highest performance. It was demonstrated that reaction pressure affected the conversion of 2-MF while the reaction temperature affected the selectivity of 2-MTHF. In addition, the structures of the spent catalysts were characterized, and mechanism of deactivation have been discussed in this work.

Microstructure evolution and impact toughness degradation of a 3.6%Si austenitic stainless steel during high-temperature exposure

Si-modified Fe–Cr–Ni austenitic stainless steel is a promising candidate structural material in lead-cooled fast reactor systems and high-temperature microstructural stability is the challenge for developing this kind of materials. In the present research, the microstructure and corresponding impact toughness evolutions of a 3.6 wt%Si austenitic stainless steel (3.6Si-ASS) aged between 510 and 650 °C up to 5000 h were investigated. It was found that the microstructure showed nearly no change within 2000 h at 510 °C. Subsequently, the G-phase (Cr3Ni2Si) began to form at grain boundaries after 3000 h. This made the matrix near grain boundaries Ni-depleted and promoted the formation of ferrite. Finally, a mixed microstructure consisting of G-phase and ferrite was formed after 5000 h. The appearance of ferrite caused a slight decrease in impact toughness. This evolution was further accelerated during aging at 550 °C, and the impact toughness showed a significant decrease when ferrite appeared. Interestingly, the G-phase and ferrite were suppressed, replaced by intergranular M6C ((Cr, Mo)3Ni2SiC) carbide and intragranular (Cr, Si, Mo)-rich χ-phase during aging at 600 and 650 °C. Herein, M6C carbides preferred to form at grain boundaries, making intergranular cracking easier and reducing the toughness. When aged at 650 °C, the higher diffusion rates of Cr, Ni, Si and Mo increase grain boundaries coverage of M6C and also the number density, diameter, and area fraction of the χ-phase.

Grain boundary diffusion and segregation of Cr in Ni [formula omitted] bicrystals: Decoding the role of grain boundary defects

Grain boundary diffusion of Cr in a near Σ11(1̄13)[110] Ni bicrystal is measured over a temperature interval between 503 K and 1203 K using the radiotracer technique. The grain boundary diffusion coefficients, Dgb, and the triple products, P=s⋅δ⋅Dgb, are determined in the C- and B-type kinetics regimes, respectively, with s being the segregation factor and δ the grain boundary width. Opposite to expectations, two distinct contributions to short-circuit diffusion along the nominally single interface are distinguished and related to the existence of two macroscopic facets with distinct grain boundary inclinations and, as a result, distinct structures. The experimental results indicate that the segregation factor of Cr in Ni is about unity, which is fully supported by ab initio calculations. Using classical atomistic simulations, Ni grain boundary self-diffusion coefficients are calculated for the symmetric and asymmetric facets. The computational simulations reveal accelerated self-diffusion kinetics along the asymmetric facet, attributing this phenomenon to the presence of disconnection-like defects. This elucidates the experimentally observed diffusion dynamics of chromium atoms, thereby corroborating the heterogeneous mechanisms governing atomic migration across distinct facets.

Influence of nickel plating on the welding metallurgical mechanism, microstructure, and shear performance of C101/80Au20Sn/C101 solder joints

Herein, electroplated and electroless plating processes were used to plate nickel (Ni) on the surface of C101 alloy, which is a low-carbon steel with a carbon content of approximately 0.1% and Fe primarily contributing to the rest of the content and which is commonly used in metal packaging, and electroplated Ni and electroless Ni C101/80Au20Sn/C101 solder joints were prepared. The welding metallurgical mechanisms, microstructures, and shear performances of the two types of solder joints were investigated through experimental observation, material characterization, shear testing, and finite-element analysis (FEA). The diffusion of Ni atoms within the two platings was evaluated using first-principles calculation. Results indicated that the atomic arrangement of the electroplated Ni layer was polycrystalline, whereas that of the electroless Ni layer was primarily amorphous. The orientation of Ni grains in the electroplated-Ni joints affected the growth of (Ni,Au)3Sn2 throughout the welding metallurgical process. The [111] orientation suppressed the growth of (Ni,Au)3Sn2, resulting in a discontinuous distribution of (Ni,Au)3Sn2 at the Ni/solder interface and considerable variations in the thickness of (Ni,Au)3Sn2. Amorphous Ni in the electroless Ni layer promoted the growth of (Ni,Au)3Sn2, resulting in a continuous (Ni,Au)3Sn2 layer having a relatively uniform thickness. The shear strength of the electroplated-Ni joints was considerably lower than that of the electroless-Ni joints. FEA results demonstrated that the locations of stress concentration in the electroplated- and electroless-Ni joints were at the (Ni,Au)3Sn2/solder interface and within the solder matrix, respectively. First-principles calculations showed that the diffusion performance of Ni atoms in the electroless Ni layer was considerably superior to that of Ni atoms in the electroplated Ni layer.

Exceptional stability of spinel Ni–MgAl2O4 catalyst with ordered mesoporous structure for dry reforming of methane

The dry reforming of methane reaction holds significant importance for the comprehensive utilization of CO2 and CH4, contributing to carbon neutrality. However, due to the high reaction temperatures, catalyst deactivation due to carbon deposition and sintering remains a challenge. In this study, a one-pot method was employed to improve the solvent evaporation self-assembly process for the preparation of Ni–MgAl2O4 catalysts. The impact of calcination temperature (600 °C, 800 °C, and 1000 °C) on the ordered mesoporous structure of the catalyst was investigated. Catalysts without an ordered mesoporous structure, such as Ni–MgAl2O4-1000, suffered deactivation due to carbon deposition caused by the large size of Ni grains, while Ni–MgAl2O4-600 deactivated due to sintering caused by the lack of confinement effect of the support on Ni. Conversely, Ni–MgAl2O4 catalysts with an ordered mesoporous structure exhibited confinement effects on Ni metal, resulting in excellent resistance to carbon deposition and sintering. Further investigation into the effect of different loading methods of Ni on methane dry reforming was conducted. A comparison was made between Ni–MgAl2O4 (800 °C) prepared by the one-pot method and Ni/MgAl2O4 (800 °C) prepared by the impregnation method. It was observed that Ni–MgAl2O4 catalysts, with Ni incorporated into the support, exhibited strong interaction between Ni and the support. During a 500-h long-term reaction, both CO2 and CH4 conversion rates remained at 90% for Ni–MgAl2O4 catalysts, with less carbon deposition and slower grain growth rate, demonstrating excellent reaction activity and stability. In contrast, the performance of Ni/MgAl2O4 catalysts gradually declined after 260 h. Ni–MgAl2O4 catalysts with ordered mesopores and strong interaction between Ni and the support displayed superior resistance to carbon deposition and sintering.

Exceptional ductility through interface-constrained grain growth for the ultrafine-scale Ni/Ni-W layered composites

Enhancing the strength of metallic laminates through decreasing the constituent layer thickness from micrometer to nanometer scale is usually accompanied by the degradation of ductility because plastic instability characterized by fatal shear bands inevitably occurs in the early stage of deformation. To overcome the strength-ductility trade-off dilemma, we designed a kind of metallic layered composites (LCs) consisting of nano-grained Ni (grain size: 21–37 nm) and ultrafine nano-grained Ni-W (grain size: 8 nm) constituent layers with layer thickness ranging from microns to tens of nanometers. We found that the strength and ductility of Ni/Ni-W LCs can be simultaneously enhanced by decreasing the layer thickness. Interface-constrained grain growth in the Ni layers with an initial layer thickness of less than 1 μm enhances strain hardening ability. Thus, strain delocalization characterized by the formation of rectangular strain zones instead of crossed micro shear bands appears in the LCs. Based on the above mechanism, we obtained the optimum ratio of the layer thickness to the grain size for the nano-grained Ni layers as about 15:1, which corresponds to Ni0.25/Ni-W0.025 LCs with the highest tensile strength (1.9 GPa) and elongation to failure (5.5 %). These findings may provide a new path for the design principle of metallic LCs with multi-level microstructural and geometrical scales.

Microstructure, wear and corrosion resistances of Ni–ZrO2–CeO2 nanocoatings

This study focused on the fabrication of Ni, Ni–ZrO2 and Ni–ZrO2–CeO2 nanocoatings using ultrasonic pulse electrodeposition. The research delved into examining the surface morphology, microhardness, abrasion, and corrosion resistance of these coatings. The results indicated that the Ni coatings displayed coarse grains and an irregular structure. Among the three, the Ni–ZrO2–CeO2 nanocoatings exhibited the most dense, flat and fine microstructure among all three coatings, and the average diameters of Ni grains, ZrO2 and CeO2 nanoparticles were 68.6 nm, 21.1 nm and 23.4 nm, respectively. The Ni, Ni–ZrO2, and Ni–ZrO2–CeO2 nanocoatings displayed high micro-hardness values, measuring an average of 363.1 Hv, 421.6 Hv, and 543.8 Hv, respectively. Moreover, the friction coefficient of Ni–ZrO2–CeO2 nanocoatings was approximately 0.31. When exposed to a 3.5 wt% NaCl solution at room temperature, the Ni–ZrO2–CeO2 nanocoatings displayed minimal corrosion damage, exhibiting the lowest corrosion rate of 0.06 mm/year compared to the other coatings. The incorporation of ZrO2 and CeO2 nanoparticles in the Ni–ZrO2–CeO2 coating led to grain size reduction and a more uniform, compact microstructure, contributing to enhanced corrosion resistance when compared to both Ni and Ni–ZrO2 coatings.

Comparative study of Ni-TaC composites via high-energy ball milling activation and spark plasma sintering: Reinforcement, densification, oxidation resistance, and mechanical property

In this study, metal matrix composites (MMCs) were produced using nickel (Ni) and tantalum carbide (TaC) powders by high-energy ball milling, and their structural characteristics and microstructural evolution against reinforcement interactions were investigated. The nominal compositions of the Ni-TaC composites were Ni (5, 10, 15, and 20) vol% TaC. The formation of the ductile-brittle (Ni-TaC) components was affected by the continued severe deformation caused by the high-energy ball milling. As a result, a Ni0.92Ta0.08 solid solution was formed, which influenced the lattice distortion and peak shift. The Ni-TaC composites were densely consolidated by spark plasma sintering at 900°C and 60 MPa. The effect of the TaC on the sinterability and mechanical properties of Ni-TaC composites was analyzed based on the shrinkage rate, densification strain, densification strain, uniform distribution of carbide phase in the Ni matrix, grain size, and morphology of crack propagation. Oxidation behavior was analyzed by scanning electron microscopy with energy dispersive X-ray diffraction. The results indicate that the formation of the NiO and TaO2 passive layer for Ni- 15 vol% TaC composites resulted in a 12 µm (thick) oxide layer. This was the thinnest oxide layer on surface at oxidation 1000°C.

Thermodynamics and kinetics of interdiffusion in Ni//NiAl diffusion couples

The growth behavior of Ni3Al after nucleation at the Ni/NiAl interface was investigated by using macroscopic diffusion couples at low annealing temperatures of 973–1073 K. The thickness and grain size of the Ni3Al phase at different annealing temperatures were statistically analyzed by scanning electron microscopy to evaluate the growth kinetics of the Ni3Al layer. According to the growth rate exponent, the growth of Ni3Al layer to NiAl is almost completely controlled by volume diffusion (VD) when it is above 1023 K, and by boundary diffusion (BD) when it is below 1023 K. In contrast, the growth of Ni3Al into Ni is controlled by VD almost whether at 1023 K or 1073 K. Remarkably, a continuous Al-rich Ni grain layer was formed at the Ni3Al/Ni interface by diffusion-induced recrystallization (DIR), and the experimental results for DIR region of composition and growth behavior were numerically analyzed using the thermodynamic and kinetic models, respectively. The analyses suggest that the composition of the DIR region in the Ni(Al) binary system can be determined by the thermodynamic conditions of the chemical driving force model (CDF model). Additionally, kinetic analysis using the new extended model (NE model) indicates that under current annealing conditions, interface reaction and BD control growth at the moving boundary of the DIR region. Furthermore, the temperature stability range of Ni5Al3 in the Ni//NiAl system was subjected to systematic analysis.

Influence of Surface Preparation on the Microstructure and Mechanical Properties of Cold-Sprayed Nickel Coatings on Al 7075 Alloy

This work presents the effect of surface roughness (Al 7075) on the microstructure and mechanical properties of cold-sprayed nickel coatings. Coating analysis included substrate surfaces and coating geometry, microstructure characterization, microhardness, nanohardness, elastic modulus, and adhesion. The results show that the surface preparation had a significant effect on coating adhesion and microstructure. The coating deposited at the highest gas temperature revealed a dense microstructure, showing very good adhesion of the impacting powder particles to the substrate and good bonding between deposited layers. The Ni grains with different shapes (elongated, equiaxed) and sizes of a few dozen to several hundred nanometres were present in the splats. An increase in temperature caused significant growth in coating thickness as a result of the powder grains’ higher velocity. Moreover, higher gas temperature resulted in the enhancement of micro- and nanohardness, elastic modulus, and adhesion. The adhesive bond strength of Ni coatings in the tested temperature ranges from 500 °C to 800 °C increased with the increase in the surface roughness of the substrate. For the Al 7075 coarse grit-blasted (CG) substrate with the highest roughness, the adhesion reached the highest value of 44.6 MPa when the working gas was at a temperature of 800 °C. There were no distinct dependencies of surface roughness and thickness on the mechanical properties of the cold-sprayed nickel coating.

Effect of different heat-treated temperatures upon structural and abrasive performance of Ni-TiN composite nanocoatings

This study reports the synthesis of Ni-TiN composite nanocoatings on a Q235 steel matrix using the electrodeposition technique, and were then treated at different temperatures. The surface morphology, structure, hardness, and abrasion performances of composite nanocoatings were investigated using scanning electron microscopy (SEM), X-ray diffraction (XRD), and friction-abrasion testing machine. SEM images illustrated smooth/dense surface morphology for Ni-TiN composite nanocoatings treated at 250 °C. XRD patterns revealed Ni and TiN phase appearance within Ni-TiN composite nanocoatings. The broader and low-intensity XRD peaks were observed for the composite following heat treatment at 250 °C, indicating the smallest size of TiN particle and Ni grain. Furthermore, Ni-TiN composite nanocoatings exhibited the highest hardness of 821 Hv following heat treatment at 250 °C. The frictional coefficient, wear rate, and indentation depth for Ni-TiN composite nanocoatings were found to be lowest at 0.45, 0.58 mg/min, and 13.8 μm, respectively after heat treatment at 250 °C. Furthermore, the Ni-TiN composite nanocoatings had peak abrasion resistance across three composite nanocoatings following heat treatment at 250 °C.

Crystallographic Study of Grain Refinement in Ni Alloys with Ni-RE Intermetallics

Rare earth-doped nickel (Ni-RE) alloys are very attractive for the neutron shielding application for excellent neutron absorption and good mechanical behavior. Ni-RE intermetallics are important for their precipitation reinforcement in Ni alloys. In this work, Ni-RE intermetallics have been founded to be Ni grain refiners, which has been proved both by nucleation crystallography analysis and experiments. Ni-RE intermetallics could work as heterogeneous nucleation well, either different in atomic structures (for example, Ni17RE2, Ni5RE, Ni7RE2, Ni3RE, Ni2RE having matching orientation relationships as (111)Ni // (0004)Ni17Gd2 with , (111)Ni // (0002)Ni5Gd with , (111)Ni // (00018)Ni7Gd2 with , (111)Ni // (00012)Ni3Gd with , (111)Ni // (222)Ni2Gd with ) or different in rare earth element (for example, (111)Ni // (0002)Ni5RE with is general matching orientation relationships (ORs) of Ni5RE (RE = Sc, Y, La ~ Lu) for Ni grains). When RE dopant mass fraction is 1 wt%, the grain size is reduced from ~50 μm to 15 μm, and the refinement effect reaches the best. The work proposes Ni-RE intermetallics as good heterogeneous nuclei for Ni grains with an atomic level understanding and provides theoretical guidance for high-strength nickel alloy design.

Anodic Performance of Ni–BCZY and Ni–BCZY–GDC Films on BCZY Electrolytes

Cermet films consisting of Ni, BaCe0.4Zr0.4Y0.2O3−δ (BCZY), and Gd0.1Ce0.9Ox (GDC), specifically, 60 wt%Ni–BCZY, 60 wt%Ni–BCZY–GDC, and 60 wt%Ni–GDC, were formed on BCZY electrolyte supports as anodes of proton ceramic fuel cells (PCFCs). The Ni grain size in these films after sintering at 1450 °C was around 2 μm. The GDC addition did not affect the Ni grain size in the case of the BCZY matrix. The anodic properties greatly depended on the oxide phase composition and worsened with increasing the GDC content. This probably occurred because of the addition of GDC, which has low proton conductivity and inhibited the proton conduction path of BCZY, reducing three-phase boundaries in the anode bulk. Since BCZY has a lower grain growth rate during sintering than BaCe0.8Y0.2O3−δ, the Ni grain growth was likely suppressed by the surrounding Ni grains containing small BCZY grains.

Tribological properties and corrosion resistance of nickel-based composite mold inserts containing lubricant nanoparticles for micro-injection molding

During the micro-injection molding process, the lifetime of mold inserts is severely limited by high-pressure impact conditions and demolding friction. To investigate the tribological properties and durability of mold insert, nickel-based composite mold inserts have been fabricated by electroforming adding polytetrafluoroethylene (PTFE), molybdenum disulfide (MoS2) and tungsten disulfide (WS2) nanoparticles, respectively. The surface morphology of pure nickel (Ni) and composite mold inserts were characterized. The Ni grain sizes of the composite mold inserts significantly decreased without changing the grain orientation and phase composition. The maximum microhardness of Ni-WS2 mold inserts was increased from 278.2 HV of pure Ni to 456.0 HV, an increase of 1.64 times, while the minimum friction coefficient against Si3N4 ball was reduced to 0.25. In addition, Ni-WS2 mold inserts exhibited excellent tribological properties, and their wear resistances were further investigated at different sliding speeds and external loads. With the increase of sliding speed and load, the self-lubricating property of the composite mold inserts would gradually disappear and the wear rate would increase significantly. The formation of a uniform and dense friction transfer film is the key to reducing the friction coefficient and wear rate. Furthermore, the corrosion resistance of the mold inserts was improved to some extent with the addition of the three nanoparticles. In dynamic electrochemical tests, the corrosion current density of Ni-PTFE mold insert was 3.083 ± 0.228 × 10−6 A/cm2 and the corrosion rate was 0.036 ± 0.003 mm/year, which showed the best corrosion resistance.

Performance of Ni–SiC composites deposited using magnetic-field-assisted electrodeposition under different magnetic-field directions

To improve the surface and structure performances of metal parts, magnetic-field-assisted electrodeposition was applied to deposit the Ni-SiC composites on Q235 steel substrates. The surface morphology, roughness, microstructure, abrasion resistance, and corrosion resistance of the composites were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), X-ray diffraction (XRD), hardness and friction wear tests, and electrochemical analysis, respectively. The Ni-SiC composite (MC-1) fabricated at 0.5 T with perpendicular magnetic direction exhibited a smooth, dense, and fine surface morphology, the highest SiC content, and a Ni grain size of only 72.3 nm. Furthermore, AFM images showed that the roughness of the MC-1 composite (Ra of 84 nm) was lower than those of Ni-SiC composites deposited at 0 T and 0.5 T. XRD analysis indicated that the application of a perpendicular magnetic field changed the preferred growth of Ni grains from the (200) to (111) crystal plane. MC-1 had the highest microhardness and lowest friction coefficient of all composites, indicating its superior abrasion resistance. Furthermore, the MC-1 composite had the lowest corrosion current (0.466 μA/cm2) and highest corrosion potential (−254 mV), indicating its superior corrosion resistance compared to the other composites.

Interface and crystallization evolution induced by reactive nitrogen and oxygen sputtering in Ni/Ti multilayer

Ni/Ti multilayers were reactively deposited with a gas mixture of Ar, N2 and O2 using the magnetron sputtering, while (N2 + O2)/Ar flow ratio during the sputtering process was varied. A detailed study on the microstructure evolution and interfacial properties was performed using grazing incidence X-ray reflectivity, X-ray diffraction, X-ray photoelectron spectroscopy, X-ray diffuse scattering, and transmission electron microscopy. With the increase in (N2 + O2)/Ar flow ratio, the grain size in Ni layers first decreases and then increases at a critical point of 25.0 %, followed with the crystal phase transforming from Ni into NiO. The mechanism of microstructure evolution in Ni layers due to N2 and O2 gas incorporation is discussed in this paper. The interfaces of Ni/Ti multilayer are smoothened due to a decrease in the size of Ni grains. Meanwhile, the interfacial effects including the vertical replication of interfacial roughness and the diffusion between adjacent Ni and Ti layers are suppressed for the N2 and O2 gas incorporation. Furthermore, the lateral correlation length of interfacial roughness varies with (N2 + O2)/Ar flow ratio, which presents the relevance with the grain size.